Hi folks Just asking the question should I be considering undersealing my 2017 roadster ??
Am I correct in thinking that the bumpers are plastic the bonnet, boot and wings are aluminium so the only steel areas are back wings and sills ? And do they not have a 12 year anti corrosion warranty - based in Manchester if I am to go ahead with it anybody have any suggestions ? Many thanks
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Hi @Barrie-Taylor ! My understanding is yes, although there is a lot of plastic and aluminium, there are still areas of the underneath with very little paint cover from the factory and the subframes are still potentially weak spots long term. The rear frame is of an open tubular construction and can therefore rot inside out. To put my money where my mouth is, my 21 plate is currently in having bilt hammer / dynatrol treatment with an Mx-5 specialist garage near Leicester. I collect tomorrow and all being well Iāll post photos. 
at the end of the day itās a long term game and weāll only know if the ND is different in 7 or so years time. But I believe most people here will say itās the same as the NC in that respect.
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Thanks for the heads up Iāll look into getting it sorted 
Yes, except damage from salt corrosion is specifically excluded in all the Mazda docs Iāve seen.
Thus in UK where we have salt on the roads the warranty is worthless.
So additional protection is needed.
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Always worth getting rust prevention treatment done. The sooner the better.
I still struggle to understand why a few manufacturers supply cars in the UK that are not really suitable for using 12 months of the year. Their corrosion warrantyās are not really worth much.
Although Iāve had mine professionally treated I just will not take it out if thereās any sign of salt.
Depends on a number of factors.
Do you plough the miles on it and drive it in all weathers?
Are you probably going to sell it and move on in a few years, no matter how much your are āin loveā with it now?
Personally I thought about it and decided against because of the following (which may or may not apply to you)
- Historically, I get bored eventually and move on. So I thought why do I want to underseal my car for the next owner to ābenefitā, when, unless sold to an enthusiast, said new āaverage joeā owner will probably do 2 mile ārunsā, park as close to the ASDA opening as possible, kick the door shut when holding the phone at one ear and shopping in another hand, drive it unsympathetically and probably not even now what underseal is.
Granted it could help with resale value if sold to the right person, but if not, I wonder if a dealer is going to whap on Ā£Ā£Ā£s to you if you say its undersealed? Same way a dealer is probably not going to give a jack if I tell them I do step 3), described below. - Iām not a fan of anyone touching my car, so when I see vids of the process underselaing entails, I cringe. (And Iām too thick to do it myself)
- As an alternative, I hose the undercarriage of my ND at least once a week in the colder months and limit drives anyway then. And after 13K miles, doing this (if it actually does help that is), the undercarriage looks fine. And Iām thinking that even if I did keep it for years, with this method (hosing the underneath, which isnāt exactly hard) and usage, will it really rust out? Again, doing this, unless sold to the ārightā owner will probably do jack all to resale value, as I suppose explaining that I do this to a dealer who cares for cars so much he sticks tyre pressures on 45psi ,would probably just result in him (rightly?) thinking Iām a sad, lifeless, friendless, loon.
So itās up to you.
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I donāt like covering everything with under seal as it looks horrid. The places that do rust easily are the cills. Wheel arches and frame rails, they rust from the inside out. Using a thin cavity wax stops them rusting but you need to be thorough injecting the cavities using a 360deg spray tube. Dinitrol ML is my choice as you donāt need a compressor a garage spray equipment. Itās very thin and creeps into tight weld seams which is where rust starts, 4 cans is enough for an Mx5.
I thought the MX 5 was all steel panels, donāt know if the later models have aluminium.
Have a look at the MX5 Restorer you tube videos, thereās lots of footage of MX5ās having surgery on the cills and arches, thatāll show you where you need to treat the cavities.
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As Iāve stated in other threads, my ND2 is a twice a week supermarket car and my toy. This being the case I can avoid taking it out in inclement weather to a large extent. However if I was using it as a daily I might consider extra protection, but not yet.
Agree with NDer too and I donāt really like people touching my car and donāt want the underside sprayed with underseal either. Iām the 2nd owner of my ND2 and in 34 months has just clocked up just 8800 milesā¦ If you use it in all weather as a ādailyā it would be worth considering options, but like everything itās personal choiceā¦
Rob
How does this affect the 12 year corrosion warranty though? If they canāt see it due to folk covering the underneath in tar like stuff, then theyāll wriggle out of it.
Must say Iād be torn if I used mine everyday, but Iāll only use it on dry days and instead just keep it clean and wiped it all down with ACF50 for now. But have thought about some better - āfit and forgetā type protection.
I think one of the corrosion protection companies makes a straw coloured wax like stuff with a rust killing additive designed for use in doors/box sections/cavities etc.
Although I am intending to do mine, I also donāt want black wax oil type stuff all over mine either, so will use this stuff when I eventually get round to doing it or having it done.
Sorry I canāt remember the name of it.
Someone on here will do hopefully
Did Ziebart ever work? Loads of BL products had this from new, with owners paying Ā£90 for the upgrade. Be careful of confirmation bias, because the rust free Maxis that pop up with the Ziebart sticker on the back window tend to single owner cars, ie. owners who took unusual car of their cars.
Iāve never really taken care of my cars (as was pointed out when I was introduced to Tom Matano at the last OC Rally in 2019). Some observations from my last couple:
- 1996 S-Special 2, imported in 2000 by TW White (the oldest UK Mazda dealership). Was mine by 2005 with about 90k kms on it. Spent the next 10 years on the commute, at one point putting on 15-20k miles a year. Underside was all original. I never did any undersealing. By 2017, and on 265k kms, it needed about Ā£1200 of welding and paint. In 2019, I relented and got Thrussington to coat the underside with something that feels like pebble dash. I probably need to rub down and dress the wishbones sometime.
- 1993 S-Limited, imported in 2004, with about 85k kms on it. The āfirstā UK owner thought he was doing the right thing, and did the full Dinitrol job; inside sills, doors. I recall fixing a lock on it in 2014, and the inside of the door was dripping with the stuff. Those first 4 years in the UK, that car was essentially a show car. Then it passed onto another owner at 100k kms for the next 5 years, used for a commute, but not huge miles. I acquired it in 2013, with about 160k kms, and over the next 5 years put on about 20k kms. In 2013, I could see a bit of bubbling on a sill. In 2018, I had all the sills and arches cut out and repaired. Underneath, the sills were worse than my 96 car, drivers side sill had essentially lost all structural integrity.
Iām not sure Dinitrol did anything to halt inevitable rusting.
None of these rust treatments are a slap on and forget kind of deal. You have to periodically inspect and redo. At Ā£200 every 2 years, over 10 years, a Ā£1000 fighting to keep rust at bay.
An elderly neighbour in Scotalnd used to steam clean the chassis of her Saab 900. The car was absolutely mint. Living in Northern Ireland, I became how hard it was to arrange a MOT there. None of this just turn up and get a test. You actually had to be organised 4 weeks in advance (when I was there). Handwashes offering chassis washes (ie a big ramp and someone cleaning the underside) were very popular (who wanted a MOT fail because the underside was dirty, MOTs there were very strict).
The disadvantages of a secondary underseal treatment is that it hides a lot. It can harden up, then seperate from the metal, creating a moisture trap, which you wonāt see until its too late. Some treatments claim to remain flexible, but then, they are applied on top of that Mazda sprayed on soundproofing; does that harden, crack?
For the fastidious owner, a steam or water clean allows early damage to be seen and nipped in the bud. Probably doesnāt cost Ā£100 a year.
My rotted sills and arches basically cost me Ā£100 a year over the length of my ownership to 2017. Now they ālookā as good as new. Probably wonāt get 21 years out f them, like the last metal. If I still have it in 10 years time, maybe by then it will be worth getting it dipped etc.
A dipped NA
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I remember my dadās Hillman Imp was given the Ziebart treatment before delivery, little yellow plastic plugs everywhere where they had drilled holes. Sills started bubbling at 9 years old.
That is Dinitrol you describe.
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Zeibart! In 1980, bought my first brand new car, a mini special, the rose metallic with beige vinyl roof option. Paid not only for Zeibart but āPolyglycoatā paint protection. Car had massive quality issues and was bought back 8 weeks into ownership! Anyway, the car had been on a 4 post lift for the Zeibart and the front floor sections used to lift it. Not only deforming the floor pan but they left 4 bare circles where the lift pucks had been! The car had to have paint to front wing too!The colour match was awful and they didnāt redo the āpolyglycoatā terrible, terrible customer service. Loads more issues but would only do my own protection since. Could not be worse than main dealers efforts!
Barrie
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Hereās a few pictures of the Dinatrol application on my Nd picked up yesterday. From the before and after ones (you can see which is which) you can see how little protection there is once the wheel arch liners are removed. The work was done by Thrussington garage near Leicester who I can thoroughly recommend as per previous posts on this forum. There was significant attention to detail, which I doubt Iād get from a non mx5 specialist.
A lot of detailed masking is performed, including gearbox diff prop shaft. The exhaust , wheel arch liners and rear bumper are removed, some key areas etch primed. Followed by application of the dinatrol including inside subframes etc. where necessary. Need to leave it for 48 hrs approx with them partly for the dinatrol to dry.
As you can tell Iām of the do it camp !
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Bilt Hamber do a clear product. Also the old traditional clear waxoyl.
Now that does look a thoroughly good job
Barrie
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Another one i didnāt add to my 1-3 post above, is that one has it done, think there '5 is a ākeeperā, only 4 months on some muppet scum on a mobile pulls out on them and writes the car off.
Iād say that is the āreferenceā underseal of many Iāve seen done.
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Individual risk perception I suppose, Iāve had 5 x MX-5ās, 3 from new, the first new one (and my first one) was showing unacceptable rust bubbling in the quarter panels at 4.5 years.
The next one (NC) needed the rear arches rebuilt around the lips at 6 years (itās tough on cars in NE Scotland in winter. The buyer of this one chose it unseen in person through the forum having been aware of it being under sealed and detailed report of the repairs.
The next one NC2 I didnāt keep long enough to get to the point of doing it and both NDās I have.
First ND was supposed to be a keeper until it wasnātā¦ these things happen 
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